1. Field of the Invention
This invention relates to a semiconductor memory device, a sector-address conversion circuit, an address-conversion method, and an operation method of the semiconductor memory device.
2. Description of the Related Art
Various kinds of memory devices including a flash memory are known. Generally, the first operation at starting of a system, reset operation and the like is performed by reading a read-only boot program and the like from a memory device.
Conventionally, a boot block used as an object for starting of a system occupies a small sector in a memory device, and is located in the high end or the low end of sector addresses (physical addresses) of the memory device (a bottom boot type or a top boot type, respectively, and called a boot block type) according to a requirement specification of the system. The two types are marketed as distinctly individual products.
FIG. 1A shows the top boot type memory device wherein a small sector 11 located at the highest sector addresses of the memory device serves as the boot block area.
FIG. 1B shows the bottom boot type memory device wherein a small sector 16 located at the lowest sector addresses of the memory device serves as the boot block area.
For an STB (set top box), there is a need to write new data while keeping data in a memory currently used in the system. That is, when there is an option service newly added and the like, it is necessary to write data or a program transmitted from a circuit to the memory device, while watching television through a television circuit.
The STB has two memory devices 20 and 25 as shown in FIG. 2. The memory device 20 is rewritten using a program stored in a boot block area 26, keeping data in the memory device 25. Further, the memory device 25 is similarly rewritten using a program stored in a boot block area 21, keeping data of the memory device 20. Thus, two memory devices are used to rewrite contents of the other memory device alternately.
Moreover, as shown in FIG. 3, a memory device that has small sectors 31 and 32 in the sectors of the highest addresses and the lowest addresses, respectively, is also available.
In addition, the boot program is stored in the lowest physical addresses of a memory device when the small sector is located in the lowest addresses of the memory device. Moreover, the boot program is stored in the highest physical addresses of a memory device when the small sector is located in the highest addresses of the memory device.
However, rewriting of the data within the same system and the like always requires to use the same boot block type from design restrictions, and rewriting between memory devices with different boot block types has a problem that it cannot be easily performed.
Moreover, a type of a memory device that has two or more banks, each having a small sector that can be used as a boot block, and rewriting each other is also marketed.
However, a problem with this type is that address areas of the boot block differ (e.g. a bank or some banks are the top boot block type and the other banks are the bottom boot block type), causing difficulties in rewriting the memory device.